Test Results of a ${\rm Nb}_{3}{\rm Sn}$ Cable-in-Conduit Conductor With Variable Pitch Sequence

The performance degradation under electro-magnetic, transverse load has grown to a key issue for the design of Nb₃Sn cable-in-conduit conductors (CICC). Beside the tolerance to bending strain of the basic Nb₃Sn strand and the void fraction of the CICC, a relevant parameter is thought to be the cable pattern. A sequence of ldquolongrdquo twist pitches in the early stages of a multi-stage cable is credited to mitigate the performance degradation compared to ldquoshortrdquo pitches. To assess quantitatively the effect of long/short pitches maintaining constant all other conductor parameters, a short length of four stages CICC is prepared, where the first half length has long pitches (83/140/192 mm) in the first three cable stages and the second half length has short pitches (34/95/139 mm). The last stage pitch is 213 mm for both lengths. The cable is made of Cr plated copper and Nb₃Sn strands with a diameter of 0.81 mm. The conductor is assembled into a SULTAN hairpin sample where the two branches have respectively long and short pitches. The DC performance, AC loss and pressure drop are measured in both conductor sections and compared to former conductors with the same design. The results are reported and the balance of advantages and drawbacks of long vs. short pitches is discussed.